In the printing industry, pictures and other non-text and text material (herein "graphic material") to be printed are formed by registering a negative with a printing plate and then exposing the same to light to form the desired image on the plate. A vacuum frame consisting of a transparent cover and a base having a surface for supporting a plurality of sheets of graphic material in registration, e.g., a photographic negative, and a printing plate, are used for this purpose. The plate is made by first placing the sheets in registration on the base surface, closing the cover, and then exposing the registered sheets of graphic material to light through the cover.
The cover is generally mounted to the base and moves with pivotal motion with respect to the support surface. Graphic material is placed upon the base support surface in registration, and the cover is lowered to meet the base support surface. After the cover is placed in initial contact with the support surface, a vacuum pump is utilized to evacuate the air from between the cover and the base support surface. In a typical prior art arrangement, the vacuum causes the base support surface to be raised to the cover, and thereby raises the graphic material to be firmly sandwiched between the cover and the base support surface. It is thus positioned for subsequent exposure to light. U.S. Pat. Nos. 3,625,611; 4,676,633; and 4,827,316 describe typical vacuum frames and their operation.
While vacuum frames provide means for firmly and positively holding graphic material in place after evacuation has been completed, it is not unusual for registered sheets of graphic material to lose their registration while the vacuum is being applied. Because the graphic material rests upon the base support surface and the base support surface is raised to meet the cover upon evacuation, the graphic material moves while the base support surface moves. The movement causes the registration of the graphic material to be disturbed in an unpredictable manner.